Prestone or something similar. There should be a white plastic overflow bottle with a with level lines for both hot and cold conditions easily visible in the engine compartment. Make sure that the green fluid levels are correct acxcording to the fill lines on the bottle and the engine temperature.

Prestone or something similar. There should be a white plastic overflow bottle with a with level lines for both hot and cold conditions easily visible in the engine compartment. Make sure that the green fluid levels are correct acxcording to the fill lines on the bottle and the engine temperature.

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Heat IS blowing out on drivers side, BUT it wont get hot ?
As long as you have heat, but not on passenger side, I would say your diverter is door is not operating, may be vacuum , or electrical, check under dash make sure no vacuum lines are leaking.

You may have air trapped in the lines to or from the heater core.
If you (still) have a real radiator cap on the radiator, remove it with a cold engine, start and run the engine allowing it to warm up while watching the water/coolant level.
Make sure the heater control is set to its highest heat setting while doing this.
If it is trapped air, you may see it 'belch' after the engine is warm and the engine thermostat is open.
Refill as needed if this is the case.
It's more difficult without direct radiator access and may require several cycles of hot/cold to allow refilling through the overflow.

Have you checked the coolant level? What you describe is exactly what happens if the coolant level is low. When stopped at idle, hot coolant is not circulating through the heater core, so no heat. As the engine increases in rpm's when you pull away from the light, the water pump is spinning quicker, and some coolant is making it to the heater core. So check the level, and if it is low, keep an eye on it to see if it drops again. That of course indicates a leak somewhere. Get it fixed, as overheating the engine leads to costly repairs and worse case a new engine. Let me know how you make out with this.

There is a recall that has something to do with the air/heat system in 2005 Dodge Grand caravans. Recall F01. Here is a link. I had mine done two weeks ago, cost me nothing. My air conditioner was overheating.